Openings in the walls of buildings, such as doors, windows, and ventilation openings, are generally provided with closure elements that permit the blocking or freeing of these openings as needed. In many cases control units are connected to the closure elements to effect a power-operated opening or closing of the openings in response to control pulses. To comply with the rules for accident prevention set forth by the leading association of employer's liability insurance companies, it is required that the regulating drives be so designed that, when there is danger of a jamming, the closing operation of the closure elements at least is immediately interrupted.
In the case of power-operated windows, doors, and gates it is known to use as control units geared electric motors which operate either with a limit on the regulating force operating by means of a built-in slip clutch or with a safety circuitry which automatically reacts to any obstacle that is present in the path of motion of the closure elements. While the slip clutches react purely mechanically to obstacles in the path of motion of the closure elements, that is, are triggered through the braking resistance caused by the particular obstacle, the safety circuitry can be made to respond through touch-contacts as well as non-contacting means, such as light barriers, Doppler radar, etc.
The electric motors usually employed as control unit drive are single or multiple-phase asynchronous motors, particularly induction or capacitor motors. Such asynchronous motors are used, because they permit practical operation in a simple manner a reliable reversal of motion to bring about motions of the closure element in opposite directions. In the case of ventilation appliances for rooms, it is likewise already part of the state of art to actuate the closure elements of the ventilation openings, such as flaps, by means of an electric asynchronous motor. The asynchronous motor is connected by means of a tightly-wound coil spring with the closure element in a driving connection, and is so arranged or developed that, when the closure element strikes an obstacle during its closing motion, it is able to stop, although the driving motion of the asynchronous motor continues until it has reached its end position corresponding to the stop position of the closure element. In order to comply with the rules for accident prevention it is necessary with all the known control unit drives described above for the use on wall openings, etc. which bring about not only a high technical expenditure, but also increase the incidence of trouble.
It is, therefore, an outstanding object of the invention to provide a safety control unit drive for wall openings in buildings, etc. that interrupts (without special precautionary measures) any specific motional operation of the closure element as soon as it strikes an obstacle in its path of motion.
These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.